Significantly Enhanced Energy Storage Density and Efficiency at Low Electric Fields in Lead-Free Bi0.5Na0.25K0.25TiO3–K0.5Na0.5NbO3 Piezoceramics Significantly Enhanced Energy Storage Density and Efficiency at Low Electric Fields in Lead-Free Bi0.5Na0.25K0.25TiO3–K0.5Na0.5NbO3 Piezoceramics AITranslate

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DOI：https://doi.org/10.1021/acsaelm.3c00607

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Bi–Na–K–TiO3 and K–Na–NbO3 lead-free piezoceramics have been widely used in next-generation advanced pulsed-power capacitors owing to their environmental friendliness and exceptional electromechanical and thermal behavior. However, the enormous challenge of obtaining ultrahigh recoverable energy storage density “Wrec” corresponding to ultrahigh efficiency “η” has persisted and has become a fundamental barrier inhibiting the development of lead-free piezoceramics in cutting-edge energy storage applications. To raise the “Wrec” and “η” substantially, we proposed a strategy to prepare a composite of lead-free bulk piezoceramics. To demonstrate the effectiveness of this approach, frequency- and temperature-dependent composites of (1–x)Bi0.5Na0.25K0.25TiO3-(x)K0.5Na0.5NbO3 (BNKT-KNN) ceramics were used as a representative in this work. (1–x)BNKT-(x)KNN piezoceramics with sub-nanometer grains (approximately 150 nm) were prepared using a solid-state reaction route followed by two-step sintering. The resultant ceramics had a dense structure with minimal pores, exhibiting pseudo-cubic symmetry and strong relaxor characteristics. The frequency- and temperature-dependent dielectric and ferroelectric properties, along with their relaxor behavior and energy storage properties, have been investigated. The large “Wrec” ∼ 40 mJ/cm3 at 10 Hz and “η” ∼ 63% at 100 Hz accomplished by applying a shallow external electric field (35 kV/cm) for 75BNKT-25KNN ceramics is comparable to other reported Bi–Na–K–TiO3- and K–Na–NbO3-based lead-free bulk ceramics. These outcomes demonstrate that the (1–x)BNKT-(x)KNN ceramics are preferred materials for advanced pulsed-power capacitors. This study paves the way to design a novel class of piezoceramic materials with high-energy storage applications to fulfill the stringent criteria of modern energy storage applications.